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Heat Protection for Turbines

In gas or steam turbines used for electricity generation in power plants or to power aircraft, a higher operating temperature and pressure results in higher efficiency, i.e. the turbines can retrieve more electrical power from each cubic metre of natural gas. This means that operating temperatures of up to 1,200°C are by no means unusual in stationary gas turbines today. However, these temperatures can only be handled if the basic metallic materials of central components are shielded against the effects of heat and corrosion by means of protective coatings.

Protective coatings currently in use are already close to reaching their limits in terms of temperature. In particular, they are not designed to be exposed to gases from alternative fuels (e.g. biofuels or hydrogen) or to rapid load changes in power plants. However, these requirements will become increasingly important in the course of the ongoing transformation of the energy sector.

Plasma BurnerA mixture of ceramic powder and water or ethanol is injected into the torch of the plasma burner and accelerated. The result is a thin protective ceramic layer on the workpiece.

Jülich researchers intend to make the protective coating systems more durable and thus ready to withstand extreme conditions, such as even higher temperatures, more frequent load changes and variable fuel compositions, for prolonged periods of time. They do so by testing new material classes and developing novel microstructures.

For example, they increase the number of small pores in thermal barrier coatings, because air pores reflect heat radiation and increase insulation – the greater the number of pores, the better heat insulation. The linchpin for higher porosity is the manufacturing process, in which ground ceramic powder is injected into the 3,000°C flame of a plasma burner, where it melts.

The thermal barrier coatings fabricated in this manner have excellent dispersion properties: up to 95% of the thermal radiation is reflected back. The scientists' goal is to achieve operating temperatures of 1,450°C for the gas turbines. For this reason, they are investigating the possibility of coating the materials currently used with an additional protective shell made entirely of newly developed ceramics.

The climate benefits from new thermal insulation systems, because if a 240-megawatt gas turbine power plant can generate 2% more electricity from the same amount of natural gas, it will produce this electricity more cheaply and will release 24,000 fewer tonnes of carbon dioxide each year.

Furnace with halogen lampsA furnace with halogen lamps in a laboratory at the Institute of Energy and Climate Research. Each of the heat-producing halogen lamps can be activated individually. This allows rapid and extreme temperature fluctuations to be simulated, which are relevant in practical applications – for example, inside power plant turbines.
Copyright: Forschungszentrum Jülich